1. Field of the Invention
The present invention relates to a lubricating system for an internal combustion engine suitable for increasing a hydraulic pressure at the time of low speed rotation up to a necessary pressure without enhancing the performance of an oil pump.
2. Description of Background Art
A lubricating system for an internal combustion engine has been known, for example, from Japanese Patent No. 2688926 entitled xe2x80x9cEngine Lubricating System for Motorcycle.xe2x80x9d
FIG. 1 illustrates an engine lubricating system in which a feed pump 22 is connected to an oil tank 8 and portions 25, to be lubricated, of the engine are connected to a discharge side of the feed pump 22 via a discharge side pipe line 24. A relief valve 27 is mounted to a halfway point of the discharge side pipe line 24 wherein lubricating oil in the discharge pipe line 24 is relieved to the oil tank 8 side when the hydraulic pressure in the discharge side pipe line 24 becomes a specific value or more, to thereby prevent the hydraulic pressure in the discharge side pipe line 24 from becoming the specific value or more.
As is known, in a rotary pump, a discharge pressure is proportional to the third power of the rotational number and is proportional to the fifth power of the diameter of an impeller.
Accordingly, in the feed pump 22 rotated by power from the engine described in the above document, when the engine speed is low, the pressure of the lubricating oil discharged from the feed pump 22 becomes significantly small.
For example, to make the pressure of the lubricating oil fed to the portions 25, to be lubricated, of the engine large even at a low engine speed, it may be conceived to increase the diameter of the impeller of the feed pump 22 or increase the rotational speed of the feed pump 22.
If the size of the feed pump 22 is made large to increase the diameter of the impeller, the size and weight of the feed pump 22 become large, and further the production cost of the feed pump is raised.
If the rotational speed of the feed pump 22 is increased, the friction of each sliding portion in the feed pump 22 becomes large, thereby degrading the pumping efficiency of the feed pump 22.
Accordingly, an object of the present invention is to provide a lubricating system for an internal combustion engine, which is capable of increasing the hydraulic pressure at the time of low speed rotation up to a necessary pressure without enhancing the performance of an oil pump.
To achieve the above object, according to the present invention, there is provided a lubricating system for an internal combustion engine, characterized in that an oil passage extending from an oil pump to a discharge port in an internal combustion engine is, at its halfway point, branched into at least two oil passages; and one of the at least two branched oil passages is provided with a restricting portion for restricting a flow amount of oil by reducing a diameter of the restricting portion, and a bypass valve which acts, when the hydraulic pressure in the oil passage exceeds a specific value, to bypass the restricting portion so as to increase the flow rate of oil.
Since one of at least two branched oil passages is provided with the restricting portion for restricting a flow amount of oil, hydraulic pressures in the at least two branched oil passages can be increased to pressures that are necessary at a low speed rotation of the engine, and when the hydraulic pressure of the one, provided with the restricting passage, of the at least two branched oil passages, exceeds a specific value, the excess increase in pressure of the oil passage can be prevented by opening the bypass valve to increase the flow rate of oil in the oil passage.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.